1. Field of the Invention
The present disclosure relates generally to determining parameters of a vehicle's wheel, steering, and suspension, more specifically, for determining suspension parameters of a racing vehicle, which include instantaneous center, roll center, roll center height, etc.
2. Description of Prior Art
There are many devices for determining parameters of a vehicle's steering and wheel. The current trend is computer projecting imagery with printout capabilities. These systems offer parameters such as caster, camber, toe, steering axis angle, included angle, setback, turning radius, scrub radius, rolling radius, and caster trail. All of these parameters can be determined by attaching devices to the outer portion of the wheel. Cameras then detect wheel orientations from the position of each device and a computer analyzes and calculates each parameter. However, these systems do not determine parameters of a vehicle's suspension such as instantaneous center, roll center, roll center height, swing arm length, and control arm length. These parameters are extremely necessary when setting up or analyzing a vehicle's suspension layout design and determining suspension linkage ratios.
Every vehicle has front and rear roll centers. Each roll center is independent from the other and are determined by suspension geometry. Roll center is the imaginary point about which the chassis tends to roll during cornering maneuvers.
The front roll center location is extremely important to the handling performance of a vehicle. The position of the roll center will determine how the suspension will react to dynamic forces, which causes the vehicle to roll during cornering. Roll center is determined at static ride height and can be changed according to the suspension's pivot locations. For example, if the left and right suspension pivot points are positioned at symmetrical locations, the roll center will be located at the center of the vehicle. The height of roll center (the vertical distance above, below, or at the ground plane) can be changed by changing the angle of the suspension's upper or lower control arm. The position of roll center can be moved to either side of the vehicle's centerline if the suspension pivot coordinates are unsymmetrical. Roll center affects the camber change characteristics of the wheel, which is critical to the vehicle's dynamic behavior characteristics.
The current measuring technique of professional race teams is to place the vehicle on a thick machined steel surface plate. This insures that the vehicle is sitting on a perfectly level surface. The suspension pivot coordinates are measured at static ride height, by hand, using a measuring tape, level, plumb bob, strings, chalk lines, or trammel.
A plumb bob is used for determining each suspension pivot location at the ground plane and a mark is placed on the surface plate representing each point. The tire's centerline and vehicle's centerline is established and also marked. Each pivot location is measured vertically from the ground plane and laterally from the vehicle's centerline. Once these coordinates are determined, they are entered into a computer program for analysis and calculations.
Getting the true height of the upper steering and frame pivot points are difficult. There are suspension components which block vertical measurements. The lower control arm blocks the upper control arm pivot points and the tire and wheel block steering pivot points that are positioned inside the wheel rim.
It is essential to measure the vehicle at static ride height, full weight on the vehicle, and the vehicle sitting on a level ground plane. But, because of the tire and wheel, which block pivot locations positioned inside the wheel rim, it is necessary for the vehicle to be raise, set on jack stands, and the wheels removed in order to access pivot locations. However, when the vehicle is raised, the control arms move downward and the vehicle is no longer at static ride height. To prevent control arm movement, the vehicle's shocks are first removed and replaced with straight rods in order to maintain static ride height. The vehicle is then raised and the wheels are removed for accessing steering pivot locations.
In order to measure the upper pivot locations which are blocked by the lower control arm, someone must improvise, such as using a small level to extend the upper pivot point out beyond the lower control arm. A height measurement from the level to the ground plane is taken. It is also necessary to improvise when determining lateral distances between upper pivot locations and the vehicle's centerline.